Clinton still has a more significant lead in the state's aggregate. According to the RealClearPolitics average of recent reputable polls, Clinton has a 5-point lead over Trump.

The Clinton campaign has focused much of its time and resources on Pennsylvania, a state whose 20 electoral votes are crucial to either candidate's path to securing the 270 electoral votes needed to win the White House.

In the last several weeks, Clinton has deployed top surrogates to the state, including President Barack Obama and first lady Michelle Obama, populist firebrand Sens. Elizabeth Warren and Bernie Sanders, and popular business leaders like billionaire investor Mark Cuban.

Recent polls show the race tightening in several other key battleground states and nationally. A Washington Post poll of national voters found the candidates in a virtual dead heat heading into their first debate Monday night at Hofstra University.

And a slew of Fox News polls released late last week found the real-estate magnate ahead in Nevada, North Carolina, and Ohio. After weeks of large Clinton leads, the RealClearPolitics average of each state now shows Trump with a slight edge in each state.